/*
The arithmetic derivative is defined by
p' = 1 for any prime p
(ab)' = a'b + ab' for all integers a, b (Leibniz rule)
For example, 20' = 24

Find ∑ gcd(k,k') for 1 &lt; k ≤ 5·1015

Note: gcd(x,y) denotes the greatest common divisor of x and y.

Anser:
Time:
*/
package main

import (
	"fmt"
	"time"
)

func main() {
	tstart := time.Now()



	tend := time.Now()
	fmt.Println(tend.Sub(tstart))
}